Um, I guess you didn't read "item switches" did you? It shows either a last whisper or atma's in there... so... I'd take a look at that before commenting.
Not to mention, in my opinion, I think thornmail is a very useful item against ADs. Especially from the damage you can put out as Lee Sin. I've done really good games. So...

You realize that you have no armor at all right?

Seems kind of silly to have that much hp and not even run an Atma's.

I see you made a comment about FoN or a Thornmail...personally I don't think thornmail is worth while. If you are gonna get an armor item, get RO or atma's

yea I agree, it is extremely hard to read. Jhoijhoi has a guide on how to make a guide that would be very useful, look that up and learn some more bbcoding. Also you should explain abilities and spells and runes and masteries so that we understand how lee sin is played. also, ive never seen a lee sin witha Force of Nature. Your build doesn't seem to highlight the strengths of lee sin and you should work to improve that. You've got a lot of work to make this build stronger but its doable. if you would like me to rereview your guide later, just pm me and ill read it again

I'd take a look at your BBCoding, because right now the huge images really break up your paragraphs and can make it somewhat difficult to read. I would start using this particular code to make your paragraphs a little more visually appealing.

[ [Name of character, item, skill] ] *Without spaces between brackets gets you Lee Sin

Hope this helps :D